1. Field of the Invention
The invention relates to hybrid or electric traction motor vehicles, and more specifically to braking systems for these vehicles, particularly braking systems allowing recovery of electrical energy.
2. Description of Related Art
Electrical energy recovery systems make it possible, during braking phases, to use the electric motor of the vehicle in order to provide deceleration, while supplying the batteries of the vehicle to increase its range.
For this purpose, decoupled brake pedal modules are used in such a way that the driver's action on the brake pedal is dissociated from the deceleration that actually takes place. In a decoupled braking module of this type, there is no direct mechanical link between the brake pedal and the braking modules, and an electric braking module or, conventionally, a hydraulic braking module can be used in order to provide the deceleration desired by the driver.
The braking system of the vehicle then sends setpoints to the electric braking module and to the hydraulic braking module, in order to provide the deceleration desired by the driver while increasing the vehicle's range.
The braking systems must also enable the stability of the vehicle and the comfort of the users to be maintained, for example by limiting pitching and jerking. Existing braking systems allowing recovery of electrical energy may, notably in certain operating conditions, send setpoints which cause switching between the electric braking module and the hydraulic braking module.
This switching may be dangerous, since, in emergency braking situations, the most effective braking system, that is to say the hydraulic braking system, must be given priority. Examples of emergency braking situations are those in which a driver has to brake to avoid an unforeseen obstacle, or in which the electric braking module is faulty.
In order to avoid an unforeseen obstacle, the driver depresses the brake pedal quickly enough to avoid the obstacle. Thus the speed at which the pedal is depressed in such a situation is higher than in a normal braking situation. If the electric braking module is faulty, the user may depress the pedal several times, more quickly than in a normal braking situation.
Thus, in emergency braking situations, the brake pedal is depressed more quickly and under greater pressure than in a normal braking situation.
Reference may be made to European Patent Application EP 2055589, which describes an energy recovery method which does not take into account the speed of depression of the pedal or the variation of pressure applied to the pedal. There has also been a proposal, in US Patent Application US 20050200 197, to calculate the braking torque, within a system operating in open loop mode and using predetermined curves. Reference may also be made to U.S. Pat. No. 6,155,365 which describes a method for controlling braking in an electric or hybrid vehicle, but which does not provide for the detection of emergency situations. Finally, US Patent Application US 20060220453 proposes a braking system comprising a regenerative braking limiting module solely for the purpose of avoiding wheel locking situations. The braking systems described in these documents therefore have the drawback of not limiting electrical energy recovery in emergency braking situations in which, for example, the driver depresses the brake pedal quickly.